Some of you might recognize this syndrome as the disease formerly known as epiphysitis. This disease--or more correctly disturbance of growth--is most commonly recognized as that problem when foals get the enlarged, often painful areas just above their knees (carpi) or hocks. But as my clients have been asking me: What is it, and what does it mean for my foal?
Physitis is simply defined as inflammation of the growth plate (physis = growth plate, itis = inflammation). Growth plates are the areas within the bones of young horses from which the bones grow or lengthen. (In adults, the plates have "closed" and are no longer present.) Technically, the growth plate is referred to as the metaphyseal growth plate. Each region of a bone has a different name, with the middle of the bone called the diaphysis, the slightly flared portions of the bone before the growth plate called the metaphysis, and the ends of the bones, where the articular cartilage is located, is called the epiphysis (see "Long Bone Anatomy" on page 63).
In young horses (where growth plates are present), the growth plate occurs within the metaphysis and becomes the line that separates the metaphysis and the epiphysis.
What Does it Mean to My Horse?
Physitis is often considered to be a developmental orthopedic disease (DOD), and as a result, it does not affect adult horses. Physitis only affects young, growing horses--more specifically, those young horses with active growth plates.
Growth plates are specialized areas within the bones of horses (and all mammals for that matter), that can be located either at one end--or in some cases both ends--of bones. Within the growth plate, there is a complex process going on called endochondral ossification, which involves the changing and maturing of cartilage cells and the replacement of cartilage by bone. By this process, the bones of the horse lengthen and the horse grows in height.
Physitis, when it occurs, usually happens at just a few of the growth plates within the young horse. Most commonly, the distal radial physis (just above the knee), the distal (lower) metacarpus or metatarsus (cannon bones), and distal (lower) tibia are affected. Externally, the growth plate might enlarge or become flared, and the foal's leg near the individual affected growth plate might take on an hourglass shape.
Clinically, foals with physitis might be overtly lame, or there could just be a perceived stiffness in gait. Some foals might not play or run quite as much as the other foals in the group. In the worst cases, the actual growth plate is warm and painful to direct palpation or pressure.
Radiographs can confirm the diagnosis and can reveal sclerosis (hardening of cartilage because of inflammation) of the areas around the growth plate (metaphysis and epiphysis). There could also be varied irregularities within the growth plate, such as lysis (rupture) or even premature closure (bone bridging across the cartilage plate).
What Causes Physitis?
There are several recognized causes of physitis; the first is nutrition. This type of physitis is seen in foals on rich pasture and/or being fed a high level of concentrates (grain). This can occur in rapidly growing foals, such as Thoroughbreds, Quarter Horses, or crosses of each.
The second type of physitis often occurs secondary to another problem, such as a flexural deformity or trauma. For example, this type of physitis can be seen in a foal with a chronic lameness in one limb; the foal bears much more weight on the opposite limb and can develop physitis in that limb. This type of physitis is due to excessive weight bearing, and the foal suffers a type of "crushing" injury to that growth plate.
Another type of physitis in horses is infectious physitis, occurring when a bacterial infection is present within the growth plate. This can be caused by a penetrating wound or can be spread hematogenously (via the bloodstream) if enough bacteria are present within the bloodstream of the foal--this is called sepsis.
How Is Physitis Diagnosed?
First, if you are suspicious that your foal has physitis, a thorough physical examination should be performed by your veterinarian. He or she will examine the foal and palpate the growth plates at the ends of the long bones, examining them for heat and/or pain. The foal should be examined for any lameness or stiffness and other potential sources for both. In addition, the foal will be examined to determine if the limbs are straight, or if an angular limb deformity has developed.
Your veterinarian will also examine the foal for any other signs related to the DOD complex, such as OCD (osteochondrosis dissecans, in which a loose cartilage fragment might be causing the problem in a joint) or flexural deformities. Radiographs might be required to determine if there are any significant abnormalities within the growth plate(s).
Physitis is also seen in young horses. Some young racehorses (especially 2-year-olds) can have problems with physitis due to the strong forces of exercise on growth plates that are still open in the distal tibia and radius.
What Do You Do?
So you have a foal with physitis--now what? The treatment depends on the cause of the physitis. Infectious physitis is probably best treated in a hospital situation, as the foal might require intravenous antibiotics and/or regional perfusion of antibiotics directly into the infected area(s). Many of these foals have a serious established infection (those with hematogenous spread), so intensive care is often warranted. The prognosis depends on the extent of the infection and whether there is any permanent bone or joint damage.
Newer therapies for infectious physitis include intraosseous catheters (catheters placed into the bone) to help distribute high levels of antibiotics directly to the area of infection. Regional perfusion is also used--this involves placing a tourniquet around the foal's leg above the infection, instilling antibiotics into a vein, and keeping the tourniquet in place for 20 minutes. This also allows very high levels of antibiotics to be concentrated in a smaller area (i.e,. the lower part of a leg vs. the whole body) to better kill bacteria and hopefully eliminate the infection without untoward effects from high doses of systemic antibiotics.
If you have a foal with nutritional physitis, especially if it's mild, you might only have to decrease the plane of nutrition. Usually just decreasing the quantity of the concentrate will help eliminate signs of physitis. Restricting exercise (not stall confinement) is also helpful. Most of the time, this type of physitis is self-limiting. In severe cases, medicating with non-steroidal anti-inflammatories (NSAIDs) such as Bute can help alleviate lameness and pain. In our practice, if a foal gets NSAIDs, then a gastroprotectant (such as GastroGard) is also administered.
In some cases, the limbs may appear deviated due to the excessive flaring of the physis and altered foot placement due to pain. The feet should be balanced at each trimming and not trimmed in an attempt to change the limb angulation. As the physitis resolves, the limb angulation will appear to return to normal unless severe physitis with bone bridging causes a growth inequity.
Foals with physitis as a result of trauma or excessive weight bearing are in a different class. If the growth plate has been damaged, then other problems might occur, such as angular limb deformities (uneven growth from the physis). Depending on the severity of these problems, surgery might be required to correct the angular limb deformity.
Physitis is usually a mild, self-limiting problem. However, its appearance in your foal might signify other problems associated with the DOD complex that could be lurking just around the corner. If you have foals or young horses you suspect have this disorder, consult with your veterinarian and evaluate your feeding program to ward off more serious growth problems in the future.
FORELIMB PHYSITIS: A Word About "Open Knees"
"Open knees" is a lay term for the growth plates just above the knees (at the distal radius), when they have not yet radiographically changed from cartilage to bone. Many times people will request radiographs to determine if the "knees are closed" as they do not want to over-stress bone that isn't fully developed.
Growth plates appear radiographically as a space between the epiphysis (bone end) and metaphysis (slightly flared part of bone at the end of the shaft; see "Long Bone Anatomy" on page 63). The uneducated can confuse them with fractures. As the horse matures, the space that was the cartilaginous growth plate ossifies (cartilage does not appear on X rays or radiographs) and becomes solid bone.
Growth plates functionally stop growing at different times in the young horse's life. For example, the distal cannon bone growth plate functionally stops growing at around 90 days. However, the distal radial growth plate will continue growing until the foal is around six to 12 months of age, with the vast majority of the growth occurring within the first six months. This is extremely important for deciding when to correct certain angular limb deformities. If corrective trimming or shoeing is not successful, then surgical treatment can only be successful as long as the growth plate involved in still active and growing.
Remember, angular limb deformities occur because of uneven growth of a growth plate and result in a bone being longer on one side than the other. Once the growth has slowed or ceased, correcting these disorders is very tough. This is because correcting serious angular limb deformities often involves placing a screw or screws and wire across one side of the affected growth plate. This is done to greatly slow, if not stop, the growth occurring on one side of a growth plate and allow the other side of the growth plate and bone to catch up. Once the leg is straight, then the screws and/or screws and wires are removed to allow growth to continue. This procedure does not work unless the growth plate is still active.
Furthermore, although the growth plate might have stopped growing radiographically, the physis can remain open (with cartilage changing to bone) for months beyond, sometimes into the horse's 2-year-old year.
In our practice this summer, a 3-month-old Thoroughbred filly was examined for suspected physitis. The main complaint was stiffness. When in the pasture with other mares and foals, she did not gallop and play, and she would not trot at all--walk and slow canter were her only gaits. The filly was being fed a 14% protein textured feed (4.5 pounds per day divided into three feedings); the mare was also on a 14% protein textured feed. They were grazed on lush pasture for 12 hours per day, and the other 12 hours they were confined to a box stall. They were also being fed a mixture of first- and second-cutting hay.
The filly was bright and alert with no fever. She was large for her age, but not fat. Her distal radial growth plates of both forelimbs were extremely enlarged and painful to direct palpation. All four feet were negative to hoof testers, and no other abnormalities could be found. Radiographs of the affected growth plates revealed marked sclerosis (hardening) of the distal radial metaphysis and epiphysis, with an irregular-appearing physis. The filly's diet was cut back to only 1 pound of grain per day, and the mare and foal were put into a smaller paddock for turnout. After one week, there was not much improvement, so the mare's grain was also decreased dramatically. Subsequently, the filly's physitis resolved completely within a few weeks and turnout was resumed into a larger paddock, at which time she was happily trotting and galloping with the other foals.--Christina S. Cable, DVM, Dipl. ACVS
- Eliis, David. "Physitis." Lameness in the Horse, Editors, Ross & Dyson. Saunders, St. Louis, 2003; 554-556.
- Turner, Simon. "Diseases of Bone and Related Structure." Adams' Lameness in Horses, Lea & Febiger, Philadelphia, 1987: 293-299.
About the Author
Christina S. Cable, DVM, Dipl. ACVS, owns Early Winter Equine in Lansing, New York. The practice focuses on primary care of mares and foals and performance horse problems.
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